The present invention relates to a spacer with a plurality of cells for retaining elongated fuel rods, arranged in parallel, into a bundle in a nuclear reactor fuel assembly. It is important that these spacers, which are placed spaced from each other along the bundle, do not form too high a resistance to the coolant flow which flows inside the fuel assembly along the bundle and through the spacers.
There are known spacers in which the cells of the spacer are formed from tubular sleeves which are composed into a so-called spacer grid for positioning the fuel rod extending through the sleeves. Each sleeve has been internally provided with fixed supports and spring means for fixing a fuel rods extending through the sleeve, the spring means being formed from a leaf spring cut out of the wall of the sleeve. Also when a fuel rod has been in position in the tubular sleeve, the leaf spring belonging to this sleeve has for the most part still extended into the sleeve. A considerable part of the space between the fuel rod and the sleeve has then been occupied by the leaf spring. This, in turn, has led to a high flow resistance through the spacer.
According to the invention, this drawback is now avoided in that the leaf spring, in tensioned position when the fuel rod is inserted into the sleeve, is returned by the fuel rod to a position substantially coinciding with the wall of the sleeve. In this way, the space between the fuel rod and the sleeve is almost entirely freed from the flow-preventing effect of the spring means.
According to a particularly suitable embodiment, the spring means is formed from a leaf spring which is cut out of the wall of the sleeve and extends transversally in relation to the longitudinal axis of the sleeve. The respective sleeve is then suitably internally provided with at least one first pair of laterally separated fixed supports at one level in the sleeve and a second, similarly arranged, pair of laterally separated fixed supports at another level in the sleeve. The spring means is arranged opposite to the fixed supports such that it makes contact with a fuel rod, inserted into the sleeve, at a point between the levels for the fixed supports.
Because the leaf spring is arranged to extend transversally in relation to the longitudinal axis of the sleeve, the leaf spring can be made sufficiently long to provide a suitably soft resilience without the length of the sleeve, and hence the flow resistance of the spacer, having to be increased.
To facilitate returning the leaf spring to a position coinciding with the sleeve wall, the leaf spring is provided at its end with a contact surface which is bent out towards the centre of the sleeve.
An additional way to improve the resilience is to design the leaf spring to be wider at its base than at its free end.
Further, the leaf spring should be cut out with as slots in the sleeve as narrow as possible to prevent lateral flow of the cooling water in the spacer.